Conventional guns and projectile launching weapons utilize the burning of chemical propellants to achieve high projectile velocity. In recent years there has been a renewed interest in projectile launchers which utilize electromagnetic energy. Such electromagnetic launchers may find application in space launched weaponry and impact fusion as well as in more conventional ordinance. Generally speaking, electromagnetic launchers promise higher projectile velocities than launchers utilizing chemical propellants.
One prior art design currently receiving considerable attention is the electromagnetic railgun. A conventional prior art electromagnetic railgun utilizes two long parallel rails capable of carrying a large current. A sliding, conducting armature is positioned between the two rails. The armature is adapted to slide between the two rails along their entire length. Application of a voltage across two ends of the two rails causes a large current pulse to flow through one rail, thence through the armature, and into the other rail. The current generates a magnetic field. The Lorentz force created by the interaction of the magnetic field with the current in the armature causes the armature to be rapidly propelled between the two rails in a direction away from the points of application of the voltage. The armature itself may be projected like a bullet at a target, or the armature may be used to push a bullet-type projectile at high velocity towards a chosen target, and the armature ultimately slowed and retained with the device for future shots.
A disadvantage of the conventional railgun is that arcing and heating may occur between the armature and rails. The heating is due to I.sup.2 R losses and the arcing is due to poor contact between the armature and rails.
Maintaining good electrical contact between the armature and the rails over the entire length of the rails without causing too much friction is a serious problem which has impeded rail gun development to date. If the contact between the armature and rails is too tight, friction slows the armature, metal fusion occurs, and degrades projectile velocity. If the contact between the armature and rails is too loose, arcing occurs.
Other embodiments of the conventional prior art railgun utilize multiple sets of parallel rails, with the sets positioned alongside each other or on top of each other and separated by insulating layers. Similarly, the armature has multiple conducting segments separated by a thickness of insulation. The multiple sets of rails are connected in series so that the armature is in a unidirectional magnetic field region. Both mutual inductance and self inductance contribute to forces on the compound armature. However, the multi-layered railgun presents more severe interfacial problems than the aforementioned single layered railgun.
Finally, another type of electromagnetic launcher, called the reconnection gun is described in an article entitled "The Reconnection Gun", by M. Cowan et. al. in Proceedings of the Third Symposium on Electromagnetic Launch Technology, April 1986. The reconnection gun consists of two rectangular coaxial coils which are spaced apart by a relatively small gap. The projectile, which is a rectangular plate, passes through the gap aimed in a direction which is orthogonal to the axes of the coils. Acceleration of the projectile is the result of magnetic field line reconnection which takes place behind the projectile as it passes through the gap. The reconnection gun, however, boils away material from the rear of the projectile, as it is accelerated, thus reducing projectile mass.